Re: [asa] Question on molecular biology and Darwinism

> If 65M years ago, after the Yucatan impact, the only mammals remaining were
> little rodents, what gene changes were necessary to take them from chipmunk to human? It would seem that there would be millions of them in order to accomplish minute changes.
>
> What might I be missing here?

"Rodent" actually refers specifically to things like mice, rats,
squirrels, guinea pigs, porcupines, etc., not to generic small mammals
such as shrews, elephant shrews, possums, rabbits, etc. The true
rodents actually appear to be relatively closely related to primates.
There's a fair amount of debate about exactly when the splits between
the major placental mammal groups occur (early Cenozoic versus
Cretaceous), obscured by the frequent use of illegitimate molecular
clock calculations.

However, none of that really makes much difference to the real point
of the question. Mammals, unlike underappreciated taxa such as
mollusks, have several complete genome sequences available, so we can
determine how many genetic changes there are between a human and a
mouse or chimp or platypus or several other things. Determining
whether, e.g., the mouse or us or both changed from the ancestral
pattern is potentially a little trickier. However, there are also
billions of people with slightly different genetic patterns, so there
is also the problem of working out exactly which differences are
really important and which aren't.

Humans are morphologically quite distinctive, corresponding to our
unique upright tailless bipedal locomotion. This involves relatively
few changes from the chimpanzee genome, but most of these seem to
relate to gene regulation. Turning things on and off at different
times or in different places, especially early in development, can
cause some drastic changes in the end product.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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